Output modules require an internal time base in order to represent fault detection mechanisms for diagnostic functions on the output module. This time base is implemented, for example, by an oscillator circuit integrated on the chip. A disadvantage of these circuits for generating the internal time base may be a high degree of imprecision. The specified range fluctuates sometimes by up to a factor of 4, for example, from 60 to 240 μs.
Furthermore, output modules are connected to a control device or a control unit, which responds to the output module, via a serial interface for data transmission, for example, to configure the module or to read out diagnostic information, as referred to German patent document no. 197 33 748.